Multi layer ceramic electronic parts having pillar-like ceramic portions

ABSTRACT

A multi-layer ceramic electronic part is made up of a laminated body in which a ceramic layer and internal electrodes laminated on one another, and external electrodes are provided at end portions of the laminated body. The internal electrodes reach to one of at least a pair of edges of the ceramic layer and oppose each other, thereby leading the internal electrodes to end surfaces of the laminated body and connecting the internal electrodes to the external electrodes. Pillar-like ceramic portions, continuous in a direction of thickness of a conductor film forming the external electrodes, are scattered in the conductor film. The ceramic portions of the external electrodes are formed so that they are continuous from an inner surface of the conductor film of the external electrodes, where they closely contact with a surface on the laminated body, up to an upper surface thereof. With this multi-layer ceramic electronic part, cracks due to heat-shock can be prevented from occurring within the laminated body, and also the property in soldering of the external electrode can be kept in good condition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to multi-layer ceramic electronic partshaving, for example, a laminated body of internal electrode patterns andceramic layers therein, at end portions of which are provided externalelectrodes so as to connect to the internal electrodes, and inparticular to multi-layer ceramic electronic parts in which a materialcommon with a ceramic material for forming the ceramic layers of thelaminated body is added into at least a portion of the externalelectrodes, and further a manufacturing method thereof.

2. Description of Related Art

As electronic components of a laminated type can be listed, for example,a laminated capacitor, a laminated inductor, a laminated piezo element,a laminated filter, a ceramic multi-layer circuit board, etc.

For example, in a laminated ceramic capacitor being the mostrepresentative one of the laminated electronic components, a largenumber of layers are stacked or laminated, each having an internalelectrode and made of dielectric material, wherein the above-mentionedinternal electrodes are pulled out to the end surfaces of the laminatedbody opposing to each other and, on the end surfaces to which thoseinternal electrodes are pulled out, are formed external electrodes, andthose external electrodes are connected to the above-mentioned internalelectrodes, respectively.

The above-mentioned laminated body 3 of the laminated ceramic capacitorhas a layer construction as shown in FIG. 3, for example. Namely, theceramic layers 7, 7 . . . , each having the internal electrode 5 or 6and made of dielectric material, are laminated in an order as shown inthe FIG. 3, and further on both sides (i.e., upper and lower sides)thereof are stacked or laminated the ceramic layers 7, 7 . . . in aplurality thereof, on which no electrode 5 or 6 is formed, respectively.Upon the end portions of the laminated body 3 having such a layerstructure therein, the internal electrodes 5 and 6 are exposed to oneanother, and as shown in FIG. 1, the above-mentioned external electrodes2 and 2 are formed at the end portions of this laminated body 3.

Such a laminated ceramic capacitor, ordinarily, is not manufactured oneby one, or in a unit of one part as shown in FIG. 3, but actually isobtained with a manufacturing method which will described below. Namely,first of all, minute ceramic powder and organic binder are mixed toprepare a slurry, and it is extended thinly on a carrier film made froma polyethylene terephthalate film, etc., by means of doctor blademethod. Then, it is dried to be formed into a ceramic green sheet. Next,this ceramic green sheet is cut out into a desired size by a cuttinghead, while being mounted on the supporting sheet, and is printed with aconductive paste on one side surface thereof by a screen printingmethod, and is dried. With this, the ceramic green sheets 1 a and 1 bare obtained, on each of which plural sets of the internal electrodepatterns 2 a and 2 b are aligned or arranged in the vertical andhorizontal directions, as shown in FIG. 4.

Next, plural pieces of the ceramic green sheets 1 a and 1 b, each havingthe above-mentioned internal electrode patterns 2 a or 2 b thereon, arestacked or laminated, and further are stacked several pieces of theceramic green sheets 1, 1 . . . having no internal electrode 2 a or 2 b,at the top and the bottom thereof. They are compressed together, therebyto form the laminated body. Here, the above ceramic green sheets 1 a and1 b are stacked on one another, on which the internal electrode patterns2 a and 2 b are shifted by half of the length in a longitudinaldirection thereof. After that, this laminated body is cut out into adesired size, thereby to manufacture laminated raw chips, and those rawchip are baked. In this manner are obtained the laminated bodies asshown in FIG. 3.

Next, this baked laminated body 3 is applied with a conductor paste onboth ends thereof and is baked, and on the surface of the bakedconductive film is treated a plating, thereby completing the laminatedceramic capacitor formed with the external electrodes at both endsthereof, as shown in FIG. 1.

The multi-layer ceramic electronic part, such as the laminated ceramiccapacitor mentioned above, is mounted on a circuit board and is solderedat the external electrodes 2 and 2 on both ends thereof on landelectrodes of the circuit board.

However, such a laminated ceramic capacitor generates thermal stresswithin the laminated body 3 due to heat-shock when being soldered at theexternal electrodes thereof or due to change of a circumferencetemperature under the condition of use after the soldering. With thisthermal stress, in particular in an end portion of the externalelectrodes 2 and 2 of the laminated body 3, can easily occur cracks. Thecracks occurring in the laminated body 3 bring about a lowering ininsulation due to invasion of moisture inside and a lowering in staticcapacitance due to discontinuity of the internal electrodes 5 and 6,thereby causing a low reliability thereof.

Such a thermal stress causing the cracks in the laminated body occursdue to the difference in the thermal expansion ratio between the ceramicmaterial, which is a main ingredient of forming the laminated body 3,and the conductor which is a main ingredient of forming the externalelectrodes 2 and 2. Then, conventionally, a measure was taken, into theconductor paste for forming the external electrodes 2 and 2 is added theceramic material of forming the ceramic layer 7 as a common material,thereby to make small the difference between the ceramic layer 7 and theexternal electrodes 2 and 2 in the physical properties, such as thethermal stress therein.

However, if the common material, i.e., the ceramic material for formingthe ceramic layer 7, is put or added into the conductor paste forforming the external electrodes 2 and 2 much, stickiness or adhesivenessof the external electrodes 2 and 2 onto the external electrodes 5 and 6comes to be inferior, i.e., connecting resistance therebetween becomeslarge and also the electric properties thereof are deteriorated. Furtherthe stickiness or adhesiveness onto the solder or Sn plating is alsodeteriorated. As a result of this, solder wetability of the externalelectrodes 2 and 2 comes to be inferior, therefore mis-mounting easilyoccurs when mounting the multi-layer ceramic electronic part(s) on thecircuit board.

SUMMARY OF THE INVENTION

An object, according to the present invention, for solving the problemin the conventional art mentioned above, is to provide a multi-layerceramic electronic parts, wherein cracks in the laminated hardly occurdue to the heat-shock accompanying a change of temperature under theconditions of being soldered and of use thereafter, and further theadhesiveness between the external and internal electrodes and theadhesiveness of solder onto the external electrode are superior, aswell, thereby also being superior in soldering property with theexternal electrodes.

According to the present invention, for achieving the above-mentionedobject, pillar-like ceramic portions 22 extending in a direction ofthickness of a conductor film 21 are scattered in the conductor films 21of the external electrodes 2 and 2. Each ceramic portion contains amaterial common to the ceramic material forming the ceramic layers 7 ofthe laminated body 3. Therefore, it has a strong bonding power onto theceramic layers 7 of the laminated body 3. On the other hand, theconductor layer 21 has a strong bonding power onto the internalelectrodes 5 and 6 of the laminated body 3, and shows a goodadhesiveness onto a plating film 24 on the surface thereof. With theconductor films 21 and the ceramic portions 22 scattered thereincomplementing each other in the characteristics thereof, it is possibleto ensure the bonding power of the external electrodes 2 and 2 at theend portions and the adhesiveness with the plating thereof, and also toprevent from occurring the cracks within the laminated body 3.

Namely, according to the present invention, there is provided amulti-layer ceramic electronic part, comprising:

a laminated body 3 in which a ceramic layer 7 and internal electrodes 5and 6 are laminated one another; and

external electrodes 2 and 2 provided at end portions of the laminatedbody 3, in which the internal electrodes 5 and 6 oppose each other andreach to one of at least a pair of edges of the ceramic layer 7, therebyleading the internal electrodes 5 and 6 to one of the end surfaces ofthe laminated body 3 and connecting the internal electrodes 5 and 6 withthe external electrodes 2 and 2, respectively. Wherein pillar-likeceramic portions 22, which are continuous in a direction of thickness ofa conductor film 21 forming the external electrodes 2 and 2, arescattered in the conductor film 21.

The ceramic portions 22, containing the common material with the ceramicmaterial forming the ceramic layers 7 of the laminated body 3, have astrong bonding power onto the ceramic layers 7 of the laminated body 3.Those ceramic portions 22 are formed so that they are continuous from aninner surface of the conductor film 21 of the external electrodes 2 and2 where it is in close contact with a surface of the laminated body 3 upto an outer surface thereof.

According to the present invention, the conductor film 21 of theexternal electrodes 2 and 2 is made of at least one metal selected froma group of Ni, Cu, Ag, Pd and Ag—Pd, and the external electrodes 2 and 2are baked at the same time as the baking of the laminated body 3.

In the multi layer ceramic electronic part, since the ceramic portions22, containing the so-called common material therein, shows a goodadhesiveness onto the ceramic layers 7 at the end portions of thelaminated body 3, the adhesiveness of the external electrodes 2 and 2can be maintained at the end portions of the laminated body 3. However,the ceramic portions 22 are in a pillar-like shape and are scattered inthe external electrodes 2 and 2, the external electrodes 2 and 2 do notadhere to the ceramic layers 7 at the end portions of the laminated body3, but rather adhere in a spot-like manner. Therefore, when a changeoccurs in temperature, the thermal stress occurring within the laminatedbody 3 is released or mitigated, accompanying the thermal expansionand/or shrinkage of the conductor films 21 of the external electrodes 2and 2, thereby hardly bringing about the cracks within the laminatedbody 3.

On the other hand, the conductor films 21 being formed to enclose aroundthe ceramic portions 22 shows a good adhesiveness with the internalelectrodes 5 and 6 at the end surfaces of the laminated body. With this,the contact resistance between the external electrodes 2 and 2 and theinternal electrodes 5 and 6 comes to be small, and at the same time, itis also difficult to cause an exfoliation of the conductor films 21 fromthe end surfaces of the laminated body 3, in particular, from theinternal electrodes 5 and 6.

Further, by baking the external electrodes 2 and 2 at the same time whenthe laminated body 3 is baked, i.e., the baking of the so-called commonmaterial, which is contained in the conductor paste for forming theconductor films 21 of the external electrodes 2 and 2, in other words,the baking of the material for forming the ceramic portions 22 of theexternal electrodes 2 and 2, is performed at the same time as the bakingof the laminated body 3. Therefore the ceramic portions 22 of theexternal electrodes 2 and 2 and the ceramic layers 7 of the laminatedbody 3 are baked as one body to obtain a strong adhesivenesstherebetween.

In addition, the adhesiveness of the plating on surface sides of theexternal electrodes 2 and 2 is also good, therefore forming a fineplating film thereon, thereby obtaining a good adhesiveness with thesolder.

As is mentioned previously, with the multi-layer ceramic electronicpart, according to the present invention, not only the adhesivenessbetween the external electrodes 2 and 2 and the internal electrodes 5and 6 at the end surfaces of the laminated body 3, but also theadhesiveness between the external electrodes 2 and 2 and the ceramiclayers 7 becomes good. Also, the adhesiveness of the plating of solderor Sn is good upon the surfaces of the external electrodes 2 and 2. As aresult of this, the wetability with solder of the external electrodes 2and 2 is also good, thereby obtaining a high strength in soldering whenthe component is mounted.

Furthermore, thermal stresses hardly occur accompanying a change oftemperature, therefore the cracks do not occur within the ceramic layers7.

Such a multi-layer ceramic electronic part, according to the presentinvention, is obtained by the following steps of:

preparing a unbaked laminated body 3;

applying and drying a conductor paste, into which is added a materialcommon with a ceramic forming the ceramic layers 7 of the laminated body3, on the edge portions of the unbaked laminated body 3;

forming the external electrodes 2 and 2 so that they connect with theinternal electrodes 5 and 6 at the end surfaces of the laminated body 3,by baking the laminated body 3; and

completing the multi-layer ceramic electronic part.

As is mentioned previously, when baking the conductor paste containingthe material common with the ceramic material for forming the ceramiclayers 7 of the laminated body 3, due to bad wetability of the conductorpowder with the ceramic particles when being melted within the conductorpaste, the ceramic particles come together by themselves to form theceramic portions 22 mentioned above, therefore they are scattered in theconductor films 21 of the external electrodes 2 and 2.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a multi-layer ceramic electronic partaccording to the present invention, a portion of which is cut out;

FIG. 2 is an enlarged cross-section view of a principle portion, inparticular showing a portion A in the FIG. 1 of the above multi-layerceramic electronic part;

FIG. 3 is an exploded view for showing the layers of a laminated body,in an example of the above multi-layer ceramic electronic parts; and

FIG. 4 is an exploded view for showing a condition of laminating ofceramic green sheets for manufacturing the multi-layer ceramicelectronic part.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, detailed and concrete explanation of the embodimentsaccording to the present invention will be given by referring to theattached drawings.

Explanation will be given on a laminated ceramic capacitor, as anexample of a multi-layer ceramic electronic part, and on a method formanufacturing thereof.

First of all, a powder of dielectric ceramic material, such as bariumtitanate, for example, is dispersed into an organic binder, such asacryl or the like and dissolved into a solvent, such as ethanol, etc.,to thereby prepare a ceramic slurry. This ceramic slurry is pasted orapplied thinly, on a base film made from a polyethylene terephthalatefilm or the like, with a constant thickness, and is dried, therebyproducing a film-like ceramic green sheet. After that, this ceramicgreen sheet is cut out into an appropriate size.

Next, as shown in FIG. 4, on the cut ceramic green sheets 1 a and 1 b,two (2) kinds of internal electrode patterns 2 a and 2 b are printed,respectively, with a conductor paste. For example, the conductor pasteis obtained by adding 100 weight % of one kind of conductor powerselected from Ni, Cu, Ag, Pd, Ag—Pd, 3-12 weight % of a binder selectedfrom ethyl cellulose, acryl, polyester, etc., and 80-120 weight % of asolvent selected from butyl carbitol, butyl carbitol acetate, terpineol,ethylcellosolve, hydrocarbon, etc., and they are mixed and dispersedequally, to be applied.

The ceramic green sheets 1 a and 1 b, on which the internal electrodepatterns 2 a and 2 b are printed, are stacked on one another, as shownin FIG. 4, and on both sides (i.e., an upper side and a lower side)thereof are further stacked with the ceramic green sheets 1 and 1, onwhich no internal electrode pattern 2 a or 2 b is printed, i.e., dummysheets, and then they are compressed to obtain the laminated body.Further, this laminated body is cut in vertical and horizontaldirections and separated into each of the chip-like laminated bodies. Inthe laminated body 3, the internal electrodes 5 and 6, opposing eachother through the ceramic layer 7, are led out to both end surfaces ofthe laminated body 3, alternatively.

On the other hand, the paste is prepared for forming the externalelectrodes 2 and 2. For this conductor paste is used one which containsone kind of conductor powder and is selected from Ni, Cu, Ag, Pd, Ag—Pd,etc., in the same manner as when applying or printing the electrodepatterns 2 a and 2 b. However, into the conductor paste is added aso-called a common material, i.e., a material common with the ceramicwhich forms the ceramic layers 7 of the laminated body 3.

For example, in a case where the conductor material contained in theconductor paste is Ni, the conductor paste is prepared by adding into100 weight % of Ni powder, 3-12 weight % of ethyl cellulose as thebinder, 80-120 weight % of the solvent, and 3-40 weight % of bariumtitanate powder as the so-called common material. If the conductormaterial contained in the conductor paste is Cu, Ag, Pd or Ag—Pd, theconductor paste is prepared in the same manner.

Next, upon both end surfaces of the unbaked laminate body, on which theinternal electrode patterns 2 a and 2 b are led out, and also covering aportion of the side surfaces of the laminated body and continuous withboth end surfaces thereof, the conductor paste mentioned above isapplied or painted, and is dried. Thereafter, by baking those laminatedbodies, the laminated bodies are baked, and at the same time is alsobaked the conductor paste forming the internal electrode patterns 2 aand 2 b and the conductor paste applied on the end portions of thelaminated body. With this, there can be obtained the baked laminatedbody 3 having the layer structure as shown in FIG. 3, and having theexternal electrodes 2 and 2 at the end portions thereof.

As shown in FIG. 3, the laminated body 3 are formed by laminating theceramic layers 7, 7 . . . of dielectric material, each having aninternal electrode 5 or 6, and further are laminated plural layers ofthe ceramic layers 7, 7 . . . on which no internal electrode 5 and 6 isformed, on both sides (i.e., upper or lower sides thereof),respectively. In the laminated body 3, the internal electrodes 5 and 6,opposing to each other through the ceramic layer 7, are led out oneanother on both end surfaces thereof. As shown in FIG. 1, by baking theconductor paste on both end surfaces of the laminated body 3 where theinternal electrodes 5 and 6 are led out, the formed external electrodes2 and 2 are connected to the internal electrodes 5 and 6.

In the manner mentioned above, when baking the conductor pastecontaining the common material with the ceramic material forming theceramic layers 7 of the laminated body 3, first the conductor powderwithin the conductor paste melts, thereafter it begins to sinter andshrink. Namely, when it comes to be the temperature of starting of thesintering of the metal powder of the conductor paste, first the meltingmetal condenses and begins to shrink. When the metal is in the conditionof melting, the ceramic particles have a bad wetability with the meltingmetal, therefore the melting metal and the ceramic particles are in thecondition that they can be easily separated from each other. When themelting metal starts condensing under this condition, the commonmaterial scattered therein is pushed out. The common material which ispushed out comes together with the particles adjacent to each other whenit comes up to the temperature of starting of the sintering of theceramic, therefore it is formed in a pillar-like shape like stitchingbetween the metal particles, and is extended to form the ceramic portion22. The ceramic portion 22 formed in this manner, one of which reachesto a surface portion of a lower ceramic layer 7 of the externalelectrodes 2 and 2 to be connected therewith, and the other of whichextends to the surfaces of the external electrodes 2 and 2. As a resultof this, it comes to be the pillar-like ceramic portion extending fromthe surface of the laminated body 3 to the surfaces of the externalelectrodes 2 and 2. This ceramic portion 22 is scattered in theconductor film 21.

FIG. 2 shows the cross-section of the external electrode 2 which isformed in this manner, in diagrammatic view, in particular, FIG. 2(a)shows an enlarged cross-section view of a portion corresponding to theportion A in FIG. 1, and FIG. 2(b) shows a view of the surface of theexternal electrode 2 corresponding to the portion B in FIG. 1. Thecondition of the external electrode 2, i.e., the cross-section and thesurface thereof can be observed by an optical microscope, and FIGS. 2(a)and (b) show the diagrammatic view thereof.

As is shown in FIG. 2, the external electrodes 2 and 2 are formed bybaking painted layers of the conductor paste on the end portions of thelaminated body 3. In the conductor layer or film 21 of the externalelectrodes 2 and 2 are scattered the pillar-like ceramic portions 22,almost equally or uniformly in a plane direction, continuous in adirection of the thickness.

In the multi-layer ceramic electronic parts, since the ceramic portions22, containing the so-called the common material therein, show a goodadhesiveness onto the ceramic layers 7 at the end portions of thelaminated body 3, the adhesiveness of the external electrodes 2 and 2can be maintained at the end portions of the laminated body 3. However,the ceramic portions 22 are in a pillar-like shape and are in thecondition of being scattered in the external electrodes 2 and 2, theexternal electrodes 2 and 2 do not adhere to the ceramic layers 7 at theend portions of the laminated body 3, but rather adhere in a spot-likemanner. Therefore, when a change occurs in temperature, the thermalstress occurring within the laminated body 3 is released or mitigatedaccompanying the thermal expansion and/or shrinkage of the conductorlayers 21 of the external electrodes 2 and 2, thereby hardly causingcracks within the laminated body 3.

Further, by baking the external electrodes 2 and 2 at the same time whenthe laminated body 3 is baked, i.e., the baking of the so-called commonmaterial, which is contained in the conductor paste for forming theconductor layers or films 21 of the external electrodes 2 and 2, inother words, the baking of the material for forming the ceramic portions22 of the external electrodes 2 and 2 is performed at the same time asthe baking of the laminated body 3. Therefore, the ceramic portions 22of the external electrodes 2 and 2 and the ceramic layers 7 of thelaminated body 3 are baked as one body.

On the conductor layer or film 21 formed in the manner mentioned above,the plating of Sn or solder is treated, and the external electrodes 2and 2 are formed. Thereby, the multi-layer ceramic electronic part iscompleted. The portion which is indicated by an imaginary two-dot chainline in FIG. 2(a) shows the solder layer.

Though the explanation was given mainly on a laminated ceramic capacitoras one example of the multi-layer ceramic electronic part in theembodiment mentioned above, however, the present invention relating to amulti-layer ceramic electronic part can be also applied to, for example,a laminated ceramic inductor, a laminated ceramic LC composite part, aceramic multi-layer wiring print board, etc.

What is claimed is:
 1. A multilayer ceramic electronic part comprising:a laminated body in which a ceramic layer and internal electrodes arelaminated on one another; and external electrodes are provided at endportions of the laminated body, in which the internal electrodes opposeeach other and reach to one of at least a pair of edges of the ceramiclayer, thereby leading out the internal electrodes to an end surface ofthe laminated body and connecting the internal electrodes to theexternal electrodes, wherein pillar-like ceramic portions are continuousin a direction of thickness of a conductor film forming the externalelectrodes and are scattered in the conductor film.
 2. A multilayerceramic electronic part as defined in claim 1, wherein the ceramicportions contain a material common with a ceramic material which formsthe ceramic layer of the laminated body.
 3. A multilayer ceramicelectronic part as defined in claim 1, wherein the ceramic portions ofthe external electrodes are formed so that they are continuous from aninner surface of the conductor film of the external electrodes, where itclosely contacts with a surface of the laminated body, up to an outersurface thereof.
 4. A multilayer ceramic electronic part as defined inclaim 1, wherein the conductor film of each of the external electrodesis made of at least one metal selected from the group consisting of Ni,Cu, Ag, Pd and Ag—Pd.
 5. A multilayer ceramic electronic part as definedin claim 1, wherein the external electrodes are baked at the same timeas the laminated body.